(Reuters) - After 14 years with Indianapolis and a season lost due to neck surgery, new Denver quarterback Peyton Manning proved he can still light up the NFL by throwing his 400th career touchdown pass and leading the Broncos to a 31-19 season-opening win over Pittsburgh.

The 36-year-old, a four-times league Most Valuable Player, threw with accuracy and strength for 253 yards and a pair of scores against the Steelers.

The quarterback's first touchdown in Denver colors, a pass to Demaryius Thomas, who sprinted home for a 71-yard touchdown, made him just the third player after Dan Marino and Brett Favre to reach 400 touchdown passes in the National Football League.

A close game turned decisively in Denver's favor late in the fourth quarter when defensive back Tracy Porter picked off Steelers quarterback Ben Roethlisberger and ran 43 yards into the end zone.

The Broncos were on top throughout the second half with Manning making good use of the no-huddle offense, a feature of his days in Indianapolis which is likely to take root in Denver too.

For Manning, who underwent four operations on his neck, it was a big first step back.

"There is always a lot of unknown going into the first week and it was a very interesting game ... our offense was very patient and I think we are still trying to form our identity and I think that will happen throughout the season," Manning told NBC television.

"Obviously it feels good, it was just one game so we have to keep it in perspective. I know how hard I've worked to get to this point and how much help I've had from a lot of people, so I am grateful for that, it's special, I'll definitely say it is special," he added.

The Broncos next face a tough trip to Atlanta, who also began their campaign in impressive fashion with a 40-24 win at Kansas City.